Earth's Disappearing Water

India's groundwater withdrawals as a percentage of groundwater recharge

(cc) NASA

Water levels in India are getting lower. They have been for some time, by as much as a foot per year for the last ten years. In the area of Haryana, Punjab, Rajasthan, and Delhi, more than 26 cubic miles of groundwater went missing between 2002 and 2008.

Why? Hydrologists -- scientists who study Earth's water, particularly its movement in relation to the land -- have found the culprit: humans.

Matt Rodell of NASA's Goddard Space Flight Center led a team of hydrologists who discovered that crop irrigation and other activities are draining the groundwater reserves faster than nature can replenish them.

Earth's groundwater originates on the surface. Precipitation and other surface waters filter down through the soil and rock, collecting in open chambers as well as in strata of sand, clay, gravel, or porous rock. But it's a process that takes time. Groundwater pumped out of the Earth for whatever reason may take years to be replenished.

The discovery that groundwater in India is being consumed by human activities was made possible by measuring minute variations in gravity, detected by NASA's GRACE satellites. GRACE is a pair of satellites that form the Gravity Recovery and Climate Experiment launched in 2002, in a partnership between NASA and the German Aerospace Center, DLR. The two satellites monitor their positions relative to each other, a position that changes in response to the pull of Earth's gravity caused by both land and water masses, including water beneath the earth's surface. When the mass of water beneath the Earth's surface changes, the gravitational pull exerted by that water also changes, enough that the GRACE satellites can measure the variance.

Co-author of the study, James Famiglietti of the University of California, Irvine, commented, "For the first time, we can observe water use on land with no additional ground-based data collection. This is critical because in many developing countries, where hydrological data are both sparse and hard to access, space-based methods provide perhaps the only opportunity to assess changes in fresh water availability across large regions."

Another co-author of the study, Isabella Velicogna of NASA's Jet Propulsion Laboratory in Pasadena and of the University of California, Irvine, added, "Using GRACE satellite observations, we can observe and monitor water storage changes in critical areas of the world, from one month to the next, without leaving our desks."

By comparing GRACE data with data shared by India's Ministry of Water Resources, the researchers were able to analyze water changes over a period of six years, revealing that groundwater use exceeded replenishment.

"We don't know the absolute volume of water in the northern Indian aquifers, but GRACE provides strong evidence that current rates of water extraction are not sustainable," cautioned Rodell. "The region has become dependent on irrigation to maximize agricultural productivity. If measures are not taken to ensure sustainable groundwater usage, the consequences for the 114 million residents of the region may include a collapse of agricultural output and severe shortages of potable water."

Could the missing groundwater be the result of natural factors, such as drought? The researchers believe not. Rainfall in the area was actually slightly higher than normal over the period of the study. Measurements of other factors including water stored in lakes and reservoirs, moisture in the soil, ice trapped in glaciers in the nearby Himalayas, and even local vegetation all indicated that the loss of water was real and attributable to only one cause: human activity.

Some people don't see the problem, perhaps because they confuse the mere existence of water with safe drinking water. There's plenty of water on Earth; 70% of the planet's surface is covered with water. Yet only about 3% of that is fresh water, and much of that is inaccessible for drinking. Making water safe to drink or transporting potable water from where it's available to where it's needed is an expensive process.

Still looking at India as an example, imagine what it would cost to desalinate and cleanse sea water from the Bay of Bengal or the Indian Ocean, and then pump it inland to the 16 million people of Delhi. That could become necessary if the region continues to lose groundwater and if the Himalayan glaciers disappear.

This issue certainly isn't unique to India. Reports of water shortages are coming out of every corner of the earth. A recent UN report warned that if the current trend continues, two-thirds of Earth's population will experience "water stress" by 2025. As indicated by Rodell's study using the GRACE satellites, the primary factor in this trend is human activity.

Simply put, if humans don't alter their behavior soon, they may dry themselves right into extinction.

Jonathan Mycroft is a freelance technology writer and fiction author, and a contributing editor for Random Notions. Read an excerpt from his novel Trial by Fear at www.jonathanmycroft.com